Cities and towns throughout the world depend on having clean potable water supplies. The dependence on clean water has increased as the population of the world has increased, especially as industrial use of rivers and lakes have become commonplace.
The explosion of world population, and corresponding increase in fresh water use, has resulted in a need to maximize water usage. However, the ability to maximize fresh water use has been limited by, (1) increased pollution of the fresh water supplies due to higher industrial output throughout the world (a direct result of the increased population); and (2) increased knowledge and standards for what constitutes clean water, acceptable for use in farming, industry, and consumption. As a result, there is a current need to increase the efficiency in the use of water, i.e., conserve existing clean water supplies, increase the current capabilities used to remove pollutants from water supplies, and increase the effectiveness of existing and new technologies to effectively treat and reach now standards in water quality.
In this light, radium, a radioactive metal that occurs naturally in rocks, soils, and ground water, has become of concern to the water supplies of many population centers throughout the world, and in particular, portions of the world where the metal is found in high concentrations, e.g., Midwestern portions of the United States, Canada, Zaire, France and portions of Russia. Of particular importance to these areas of high radium concentration, is the fact that radium readily dissolves in the acidic environment of ground water, and is often found as a major natural pollutant in these water supplies.
Radium, an element of group IIA of the periodic table, having 14 radioactive isotopes, continuously releases energy into the environment until a stable, non-radioactive material is formed. Conversion of radium, for example radium-226, to a stable, non-radioactive element, for example lead-206, occurs by radioactive decay, for example, through the emission of alpha-particles. During the process, other radioactive isotopes, for example radon-222, form from the original radium. Radium-226 has a half-life of 1,620 years, an indication that the isotope, once in the water supply, will remain radioactive in the water supply until removed (for all practical purposes). In addition, it is important to note that radioactivity is not dependent on the physical state or chemical combination of the material, requiring a radioactive material to be physically removed from the water supply in order to free it of the radioactivity.
The level of radioactivity in a water supply is determined by measuring the different characteristics of energy released within the water. Radioactivity is usually measured in units called “curries” (Ci), and its metric multiplies and fractions, for example, the mega, kilo, milli, micro, and picocurrie. It is well established that a curie is 3.37×1010 disintegrations per second. With regard to drinking water, radioactivity is extremely low and is measured in picocurries (one picocurrie equals one-trillionth of a curie) per liter (pCi/L) or gram (pCi/g) of tested material.
There are several known steps used in determining the level of radium in a water supply. Typically, the first step is to perform a “short-term gross alpha test” (gross meaning total) on a sample of the water supply. Most naturally occurring radioactive elements, like radium, emit alpha particles as they decay, and radium is no exception. Detection of alpha particles in the water signals the presence of specific radioactive substances, and provides a signal that further testing may be required, and that radium is likely present in the water supply (although other alpha emitting radioactive materials may be present in the water, radium represents a major element of concern due to its widespread distribution, especially in the regions of the world discussed above).
The United States Environmental Protection Agency (EPA) has established Maximum Contaminant Levels (MCL) for combined radium-226 and radium-228, and for other gross alpha emissions in drinking water. These MCL are based on current standards of safety with regard to alpha radiation, based on the relative risk of the emissions to the safety of the consuming population of the water. As such, the MCL represents the maximum permissible level of, in this case alpha emissions, that ensures the safety of the water over a lifetime of consumption, taking into consideration feasible treatment technologies for removing radium and other alpha emitters from the water and for monitoring capabilities of these same materials. The MCL for combined radium-226 and radium-228 is 5 pCi/L of water. In addition, the MCL for gross alpha in drinking water is 15 pCi/L (note that specific MCLs for radium-224 or other specific alpha emitters have not been established).
Presently, there are a number of water sources that violate the EPA's MCL for radium. This remains the case even-though these water sources are processed through state of the art water treatment facilities. For example, as of May of 2001, approximately 200 water treatment facilities in a 20 state area were in violation of the mandated MCL for radium. In particular, Illinois had almost 100 facilities in violation of the EPA's standards. It is believed that the number of radium standard violations is likely to reach 250 to 300 facilities once a more comprehensive determination of radium levels is performed throughout the United States.
Presently, drinking water treatment facilities in the United States are searching for ways to lower radium levels to comply with the MCL (this applies world wide as well where many countries are attempting to lower radium levels in the drinking water supplies) in a cost effective manner. State of the art solutions include point-of-use technologies, such as reverse osmosis or carbon absorption filters. Larger scale solutions include relatively expensive ion-exchange resins that require the spent resins to be recovered and the radium to be isolated from the resin and disposed of in highly concentrated fashions, i.e., high-level waste. As is well known in the art, high-level waste must be disposed of at highly regulated licensed sites, at exorbitant cost.
As such, there is a need for a radium removal system from water that is relatively inexpensive and allows for the disposal of the collected radium at low-level radioactive waste sites. Note that low-level waste sites typically are characterized as receiving waste having less than 10,000 pCi/g in the material. The inability to remove radium in a condition for low-level radioactivity disposal has traditionally been a major drawback of existing radium removal technology. Against this backdrop the present invention was developed.